How to create Coffee with Foam?
You need to enable auto-smooth normals. The reason why the coffee is being shaded so weirdly is because you've enabled smooth shading which averages out the normals. As a result, some of those flat faces start getting the strange shading as if they were a curved surface.



So go to Mesh Data > Normals > and enable Auto Smooth. Then increase the angle slightly so that all of the rounded faces that should be smoothed out are smoothed out. However, if you increase it too much, it'll start smoothing out the top face again and you'll end up with the strange shading again.



Edit:

You also seemed to have forgotten to delete some of the geometry from the cup object. that intersecting with the liquid is probably part of the reason why it looked so weird. And please turn down the viewport subsurf modifier on the cup down from 6...there is no reason why that cup should have millions of verts.